1. Field of the Invention
The present invention relates to the field of bearing structures for rotatable shafts subjected to radial and axial loads, and in a particular aspect to turbocharger bearing structures.
2. Description of the Prior Art
A number of bearing structures have been proposed for use with rotatable shafts which are also subjected to axial thrust loads. When the shaft rotates at high speeds, the problems encountered with such bearing structures are significant. One particular field in which bearing structures have been proposed for shafts rotating at very high speeds is in the field of turbochargers. The shafts for turbochargers may exceed 150,000 revolutions per minute, and it is important under these circumstances to provide a bearing structure which is simple in construction and easily serviced, but at the same time is durable and will assure proper rotation of the shaft.
In U.S. Pat. No. 3,993,370, issued to Woollenweber on Nov. 23, 1976, there is disclosed a lubricated bearing structure. The Woollenweber patent describes as prior art a bearing assembly which employs a full sleeve tubular bearing rotatably located in a sleeve section of the bearing housing and encircling the shaft. When thrust is transmitted in one direction, the thrust is applied to the sleeve bearing and from the sleeve bearing to a stationary thrust plate. Since the sleeve bearing rotates at a speed less than the shaft speed, the thrust is transmitted between portions which have a lower speed differential than that which exists between the shaft and the stationary plate. However, it is further described that when thrust is transmitted in the opposite direction, the thrust is transmitted from a collar secured to the shaft directly to the thrust plate, thus transmitting the thrust between one portion travelling at the rotational speed of the shaft and a stationary portion. In this respect, inefficiency results and this is considered to be disadvantageous.
The Woollenweber disclosure also relates to a bearing structure which employs two bearings instead of a single sleeve bearing. Separate stationary bearing surfaces are provided for each of the bearings. In this manner, the Woollenweber bearing structure provides for the transmission of a thrust load, in either direction, between members which have a lower speed differential than that which exists between the shaft and stationary plate. In either direction, the thrust load is applied from the shaft to the bearing traveling at a speed less than that of the shaft, and then from the bearing to the stationary bearing plate. In the Woollenweber bearing structure, the stationary bearing surfaces are provided as fixed annular flanges forming a portion of the bearing housing.
A similar bearing structure is shown in U.S. Pat. No. 3,734,650, issued to Reisacher et al. on May 22, 1973. The Reisacher bearing structure differs from that shown in the Woollenweber patent in that the rigid bearing flanges are replaced with a thrust bearing fit within the bearing housing between the pair of sleeve bearings. In either direction, the thrust load is transmitted from the shaft to the bearing sleeve and then from the bearing sleeve to the central thrust bearing.
A similar construction is also shown in U.S. Pat. No. 774,415, issued to Conrad on Nov. 8, 1904. The Conrad patent relates to a vehicle wheel and axle, and describes a housing including a reduced-diameter center portion. The shaft is received through the housing and bearing sleeves are positioned in the housing on opposite sides of the reduced-diameter portion. Thrust loads may be transmitted from the axle to the bearing sleeves and from there to the reduced-diameter portion of the housing.
The present invention provides a bearing housing which in a particular aspect provides a thrust bearing sleeve which is movable within the bearing housing to accommodate movement of the shaft and the bearing sleeves. When the latter occurs, the rigid thrust bearings in the prior art will have their end bearing surfaces non-parallel with the end bearing surfaces of the sleeve bearing. This misalignment will result in poor load carrying capacity of the thrust bearing elements, and is therefore disadvantageous.